The Office® suite of software, from Microsoft®, is the most widely
used for working with Word, Excel, and PowerPoint files. Microsoft also offers
"Viewer" software for Word, Excel, and PowerPoint files at no monetary
cost to you. Please visit Microsoft's
Office Web site.

PDF (.pdf) — Platform-independent, lightweight files used for distributing
documents that retain a high degree of visual fidelity to the original source
document, including business letters, forms, and digital graphics.

Adobe® Reader® is the most widely distributed software for viewing .pdf
files; it is available at no monetary cost to you on Adobe's
Web site.

ZIP (.zip) — "Archive" files
that hold one or more other files and also compress the file size of these.
To access the contents of a .zip file, you must decompress it. (More
.zip information from Wikipedia.org)